Protection of Mice and Nude Rats Against Toxoplasmosis by an Octameric Construct of the P30 48–67 Peptide

Abstract

The sequence of the first 20 NH2-terminus residues of P30 were obtained from this major surface antigen of T. gondii purified by HPLC. A synthetic peptide (P30 48–67) has been prepared both in linear form and as an octameric construction. Immunization of mice and rats with the P30 48–67 octamer in the presence of IFA induces high levels of IgG antibodies which recognize both the monomelic and the octameric peptides in ELISA, and P30 in Western blots of NP40-extracted tachyzoite antigens. Since these sera are negative in immunofluorescence assays with whole tachyzoites, it seems that IgG antibodies induced by P30 48–67 octamer, although recognizing the denatured structure, are unable to recognize the native protein. The protective effect of both constructs has been studied in mice and Nude rats. Whereas immunization of mice with the monomelic peptide does not confer any protection against oral infection with 1200 cysts of T. gondii 76K strain (mortality within 11 days), 40% of mice immunized with the octameric construct survived up to 75 days after infection. Nude rats were passively transferred with 5 x10⁴ T lymphocytes from P30 48–67 octamer-immunized Fischer rats before infection with 5 x 10⁴ RH strain tachyzoites. When compared to Nude rats transferred with control T lymphocytes, they presented an almost two-fold increase in their mean survival time and raised an intense IgG antibody response against P30. This shows that immunization with P30 48–67 MAP also induces an efficient T cell immune response.